The present invention relates in general to machines for working panels by removing material and in particular to wooden panel sanding machines.
Up to the present time, industrial sanding machines for wooden panels comprise a power-driven pad, in the form of a bar, that is mounted horizontally over the worktable of the machine on which the panels move forward horizontally and that is equipped with an abrasive belt.
The pad is placed across the worktable of the machine and is supported by two vertical high-speed power spindles driven by a single motor, which drives the two spindles through a toothed belt, which synchronizes their operation. The spindles rotate eccentrically about an axis transverse to the machine worktable.
The orbital motion of the pad allows the abrasive grit on the belt to work the surface of the panel in crisscross fashion. This type of sanding enables the part to be finished better and, when working wooden parts with uprights and crosspieces, where, obviously, the grain directions of the wood cross each other, it permits smoothing of the wooden surface without leaving ugly crossmarks, thus solving a major problem with older generation machines.
The pad is equipped with means for fixing and tensioning the abrasive belt. The belt, which consists of a rectangular strip, is attached with its long sides to the specially shaped sides of the pad and kept tensioned on the pad by a cushion of compressed air blown through special pipes located between the pad and the belt.
During operation, the abrasive belt is pressed against the panel and the sanding action is provided by the combined effect of the thrusting and orbiting motion applied by the pad.
At present, the abrasive belt is changed by hand, resulting in downtime which has negative effects on the economy of the process.
Moreover, since the diameter of the pad's orbit is in the order of just a few millimeters, the dust that accumulates as material is removed from the panel cannot be eliminated until the panel leaves the area where it is in contact with the abrasive belt. Even then, since the dust is removed only by the effect of gravity, the amount of dust eliminated is limited.
The elimination of dust from the abrasive belt is therefore difficult and unsatisfactory. Moreover, since sanding belts typically have a fine grit size with a high number of abrasive particles per unit of surface area, they tend to become easily clogged up with dust which reduces their cutting efficiency. Consequently, to achieve satisfactory machining quality, the abrasive belt must be changed frequently, resulting in further negative effects on the economy of the process.
Another disadvantage is that the abrasive belts have to be specially designed and made according to the fixing and tensioning devices of the pads to which they must be fitted.
The disadvantages described above have recently a become even more critical on account of the development of sanding machines equipped with two orbiting heads placed in line along the panel feed path. In these, the use of a blower located between the two heads to clean at least the surface of a panel as it leaves the first head and before it is fed to the other head, has proved to be a temporary and unsatisfactory solution to these problems.
The aim of the present invention is to overcome the above mentioned disadvantages by providing a solution whereby the abrasive belt is changed automatically and which, by effectively eliminating the dust from the abrasive belt, renders sanding machines more productive and economical to run.